This proposal describes a series of expansion projects designed to supplement on-going studies in the general area of thrombosis by the eight principal investigators who presently comprise a Thrombosis Reserch Program Project. Thus, the group of eight clinical and basic scientists is already engaged in a variety of studies dealing with the biochemistry and physiology of blood platelets and clotting proteins, as well as bio-compatible materials and thrombogenic surfaces. Most of the projects described in the application are logical outgrowths of existing programs. In some cases rapid progress in the proposed areas has opened up entirely new vistas. These include detailed studies on fibrin formation, new synthetic anticoagulants and plasminogen activators, and a hitherto unexpected activity for platelet factor 4. In one case, funds are requested for the characterization of what appears to be a new clotting factor (Passavoy factor), and in another funds are being sought to expand a biomaterials study to include electron microscopy. The existing Program Project involves a number of collaborative investigations among the eight principal investigators, who are themselves members of four different departments and represent a variety of disciplines. The supplementary requested funds would strengthen these interdisciplinary efforts and enhance the ties between basic research and clinical application.